Single-compartment electrolytic hydrodimerization process

ABSTRACT

In a process for hydrodimerizing an olefinic nitrile, amide or ester by electrolyzing an aqueous solution of the olefinic compound, quaternary ammonium or phosphonium ions and an alkali metal phosphate, borate or carbonate in a single-compartment cell, anode corrosion is substantially lessened by use of a cell having an anode consisting essentially of carbon steel. Even at relatively high temperatures and current densities, corrosion of such an anode is surprisingly slow. Even lower rates of corrosion of such an anode are achieved when the electrolyzed solution contains an alkali metal phosphate and an alkali metal borate.

United States Patent [191 Heckle et al.

[4 1 July 29,1975

1 1 SINGLE-COMPARTMENT ELECTROLYTIC HYDRODIMERIZATION PROCESS [75] Inventors: William A. Heckle; Donald L.

Sadler, both of Pensacola, Fla.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Aug. 15, 1974 [21] Appl. No.: 497,800

Related U.S. Application Data [63] Continuation-impart of Ser. No. 385,766, Aug. 6, 1973, abandoned, and a continuation-in-part of Ser. No. 284,372, Aug. 28, 1972, abandoned.

[52] U.S. Cl 204/73 R; 204/73 A; 204/293 [51] Int. C1. CZSB 3/10; C25B 11/04;

C07C 120/00; CO7C 103/14 [58] Field of Search 204/73 R, 73 A [56] References Cited UNITED STATES PATENTS 3,375,237 3/1968 Baizcr et al 260/887 3,402,1 12 9/1968 Brubaker et a1. 204/73 A 3,511,765 5/1970 Beck et a1 3,616,321 10/1971 Verheyden et al. 204/73 A 3,689,382 9/1972 Fox et al 204/73 A Primary ExaminerF. C. Edmundson Attorney, Agent, or FirmGeorge R. Beck [57] ABSTRACT 27 Claims, No Drawings SINGLE-COMPARTMENT ELECTROLYTIC HYDRODIMERIZATION PROCESS CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our now abandoned copending application Ser. No. 385,766 filed Aug. 6, 1973, and a continuation-in-part of nowabandoned application Ser. No. 284,372 which was filed on Aug. 28, 1972.

BACKGROUND OF THE INVENTION Production of paraffinic dinitriles, dicarboxamides or dicarboxylates by electrolytic hydrodimerization of an alpha, beta-olefinic nitrile, carboxamide or carboxylate is well known, eg from U.S. Pat. Nos. 3,193,475-79 and 3,193,481-83 issued July 6,1965, to M. M. Baizer. Although the process has been sufficiently attractive that it has been in commercial use for over nine years, efforts to develop improvements thereon have been continued with particular emphasis on lowering electric power costs and mitigating electrode corrosion and fouling tendencies because of which it has been heretofore commercially preferable to carry out the process with a cell divided by cation-permeable membrane into separate anolyte and catholyte compartments. With the object of maintaining high electrolyte conductivity while employing a relatively low proportion of organic salts in the elctrolysis medium, one approach to improvement of the process has been to carry out the electrolysis in an aqueous solution of a mixture of quaternary ammonium and alkali metal salts together with the olefinic compound to be hydrodimerized.

An example of a process utilizing such an approach is described in U.S. Pat. No. 3,616,321 issued Oct. 26, 1971, to Albert Verheyden et a1. As described in that patent, adiponitrile is produced by electrolyzing an aqueous emulsion of acrylonitrile, an acidic alkali metal salt of a polyacid such as phosphoric acid and a surface-active substance such as a quaternary ammonium salt. According to that patent, selectivities on the order of 75-83 percent can be achieved when such a process is carried out in a single-compartment (undivided) cell having a graphite cathode and an iron or magnetite anode. However, corrosion of that type of anode proceeds at such a high rate that even with the use of an anode corrosion inhibitor such as an alkali metal pyrophosphate or metaphosphate, the process must be carried out at such low temperatures (preferably about 20C.) that expensive refrigeration of the electrolysis medium is required and at low enough current densities (typically less than 0.1 amp per square centimeter of anode surface area) that the productive capacity of such a cell is quite low. The suitability of other materials (e.g. nickel, lead, lead dioxide, stainless steel and alloy steel) for use as the anode in similar processes has been suggested in U.S. Pat. No. 3,511,765 issued May 12, 1970, to Fritz Beck et al., U.S. Pat. No. 3,630,861 issued Dec. 28, 1971, to Jean Bizot et al. and U.S. Pat. No. 3,689,382 issued Sept. 5, 1972, to Homer M. Fox et al. However, the materials just mentioned are likewise subject to relatively rapid corrosion when used as the anode in processes of the kind just mentioned.

To avoid the costs of using a cell-dividing membrane and for other reasons including those referred to hereinbefore, a process by which an olefinic nitrile, carboxamide or carboxylate can be electrolytically hydrodimerized in an undivided cell with high selectivity and a low rate of anode corrosion is highly attractive for commercial use. Accordingly, the provision described such a process is an object of the invention sescribed herein. Other objects of this invention are to provide such a process which can be carried out at relatively high temperatures and/or current densities and with a comparatively inexpensive anode material having high electrical conductivity and good mechanical properties. Further object of the invention will be apparent from the following description and Examples in which all percentages are by weight except where otherwise noted.

SUMMARY OF THE INVENTION It has now been discovered that an olefinic compound having the formula R C=CR-X wherein -X is -CN, -CONR or -COOR, R is hydrogen or R and R is C -C alkyl can be hydrodimerized in an undivided cell with high selectivity for the desired hydrodimer and a surpirsingly low rate of anode corrosion by electrolyzing an aqueous solution of the olefinic compound, quaternary ammonium or phosphonium ions and an alkali metal phosphate, borate or carbonate in an undivided cell having an anode consisting essentially of carbon steel. In one embodiment, the process of this invention is carried out by electrolyzing in such a cell an aqueous solution having dissolved therein at least about 0.1 percent of the olefinic compound, at least about 10 gram mol per liter of the quaternary ammonium or phosphonium ions and at least about 0.1 percent of the alkali metal phosphate, borate or carbonate. Especially low rates of corrosion of such an anode are achieved when the electrolyzed solution contains at least about 0.5 percent of alkali metal phosphate and at least about 0.25 percent by weight of alkali metal borate. The invention is particularly useful in the preparation of adiponitrile, a nylon 66 intermediate, by the hydrodimerization of acrylonitrile.

DETAILED DESCRIPTION OF THE INVENTION Olefinic compounds that can be hydrodimerized by the process of this invention include those having the structural formula R C=CR-X wherein -X is -CN, -CONR or -COOR, R is hydrogen or R and R is C -C alkyl (i.e., methyl, ethyl, n-propyl, isopropyl, nbutyl, isobutyl or tert-butyl). Compounds having that formula are known as having alpha-beta monounsaturation and in each such compound, at least one R may be R while at least one other R is hydrogen and at least one R, if present, may be an alkyl group containing a given number of carbon atoms while at least one other R, if present, is an alkyl group containing a different number of carbon atoms. Such compounds include olefinic nitriles such as, for example, acrylonitrile, methacrylonitrile, crotononitrile, 2- methylenebutyronitrile, 2-pentenenitrile, 2- methylenevaleronitrile, 2-methylenehexanenitrile, tiglonitrile or 2-ethylid'enehexanenitrile; olefinic carboxylates such as, for example, methyl acrylate, ethyl acrylate or ethyl crotonate; and olefinic carboxamides such as, for example, acrylamide, methacrylamide, N,N- diethylacrylamide or N,N-diethylcrotonamide. Best results are generally obtained when the olefinic compound has at least one hydrogen atom directly attached to either of the two carbon atoms joined by the double bond in the aforedescribed structural formula. Also presently of greater utility in the process of this invention are those olefinic compounds where R is methyl or ethyl, and particularly acrylonitrile, methyl acrylate and alphamethyl acrylonitrile. Products of hydrodimerization of such compounds include those having the structural formula X-CHR-CR -CR -CHR-X wherein X and R have the aforesaid significance, i.e., paraffinic dinitriles such as, for example, adiponitrile and 2,5- dimethyladiponitrile; paraffinic dicarboxylates such as, for example, dimethyladipate and diethyl-3,4- dimethyladipate; and paraffinic dicarboxamides such as, for example, adipamide, dimethyladipamide and N,- N'-dimethyl-2,S-dimethyladipamide. Such hydrodimeres can be employed as monomers or as intermediates convertible by known processes into monomers useful in the manufacture of high molecular weight polymers including polyamides and polyesters. The dinitriles, for example, can be hydrogenated by known processes to prepare paraffinic diamines especially useful in the production of high molecular weight polyamides. Other examples of various olefinic compounds that can be hydrodimerized by the process of this invention and the hydrodimers thereby produced are identified in the aforecited U.S. Pat. Nos. 3,193,475-79 and '481-83.

The invention is herein described in terms of electrolyzing an aqueous solution having dissolved therein certain proportions of the olefinic compound to be hydrodimerized, quaternary ammonium or phosphonium ions and an alkali metal phosphate, borate or carbonate. Such use of the term aqueous solution does not imply, however, that the electrolysis medium may not also contain an undissolved organic phase. To the contrary, the process of this invention can be carried out by electrolyzing the aqueous solution in an electrolysis medium containing the recited aqueous solution and a dispersed but undissolved organic phase in any proportions at which the aqueous solution is the continuous phase of the electrolysis medium. Hence in some embodiments of the invention there may be suitably electrolyzed an aqueous solution containing essentially no undissolved organic phase, by which is meant either no measurable amount of undissolved organic phase or a minute proportion of undissolved organic phase having no significant effect on the hydrodimer selectivity achieved when the aqueous solution is electrolyzed in accordance with the process of this invention. Such a minute proportion, if present, would be typically less than 5 percent of the combined weight of the aqueous solution and the undissolved organic phase contained therein. In other embodiments, the invention can be carried out by electrolyzing the aqueous solution in an electrolysis medium consisting essentially of the recited aqueous solution and a dispersed but undissolved organic phase in a large proportion (e.g. up to about percent, percent or even more of the combined weight of the aqueous solution and the undissolved organic phase in the electrolysis medium) which may or may not significantly affect the hydrodimer selectivity depending on other conditions of the process. In some continuous process embodiments involving recycle of unconverted olefinic compound and whether present in a minute or larger proportion, such as organic phase would be normally made up mainly (most commonly at least about 65 percent and even more typically at least about 75 percent) of the olefinic compound to be hydrodimerized and hydrodimer product with some minor amounts of organic hydrodimerization byproducts, quaternary ammonium or phosphonium ions,

etc. possibly also present. Typically, such an organic phase contains at least about 10 percent, preferably between about 15 percent and about 50 percent, and even more desirably between about 20 percent and about 40 percent of the olefinic compound to be hydrodimerized. In any event, however, the concentrations of the constituents dissolved in the aqueous solution to be electrolyzed, as set forth in this specification and the appended claims, are with reference to the recited aqueous solution alone and not the combined contents of said aqueous solution and an undissolved organic phase which, as aforesaid, may be present but need not be present in the electrolysis medium as the process of this invention is carried out. On the other hand, the weight percentages of undissolved organic phase described herein are based on the combined weight of the aqueous solution and the undissolved organic phase in the electrolysis medium.

Referring to the constituents of the aqueous phase, the olefinic compound to be hydrodimerized will be present in at least such a proportion that electrolysis of the solution, as described herein, will result in a substantial amount of the desired hydrodimer being produced. That proportion is generally at least about 0.1 percent of the aqueous solution, more typically at least about 0.5 percent of the aqueous solution and, in some embodiments of the invention, preferably at least about 1 percent of the aqueous solution. Inclusion of one or more additional constituents which increase the solubility of the olefinic compound in the solution may permit carrying out the process with the solution containing relatively high proportions of the olefinic compound, e.g. at least about 5 percent or even 10 percent or more, but in many embodiments of the invention, the aqueous solution contains less than about 5 percent (e.g. not more than 4 percent) of the olefinic compound and, in some of those embodiments, preferably not more than about 1.8 percent of the olefinic compound.

The minimum required proportion of quaternary ammonium or phosphonium ions is very small. In general, there need be only an amount sufficient to provide the desired hydrodimer selectivity (typically at least about percent) although much higher proportions can be present if desired or convenient. In most cases, the quaternary ammonium or phosphonium cations are present in concentration of at least about 10 gram mol per liter of the aqueous solution. Even more typically their concentration is at least about 10' gram mol per liter of the solution. Although higher proportions may be present in some cases, as aforesaid, the quaternary ammonium or phosphonium cations are generally present in the aqueous solution in a concentration not higher than about 0.5 gram mol per liter and even more usually, in a concentration not higher than about 10' gram mol per liter. In some preferred embodiments, the concentration of quaternary ammonium or phosphonium ions in the solution is between about 10 and about 10' gram mol per liter.

The quaternary ions that are present in such concentrations are those positively charged ions in which a nitrogen or phosphorous atom has a valence of five and is directly linked to other atoms (e.g. carbon) satisfying four fifths of that valence. Such cations need contain only one pentavalent nitrogen or phosphorus atom but may contain more than one such pentavalent atoms as in, e.g., various multivalent multi-quaternary ions such as the bis-quaternary ammonium or phosphonium ions referred to hereinafter. Suitable mono-quaternary ions may be cyclic, as in the case of the piperidiniums, pyrrolidiniums and morpholiniums, but they are more generally of the type in which a pentavalent nitrogen or phosphorus atom is directly linked to a total of four monovalent organic groups preferably devoid of olefinic unsaturation and desirably selected from the group consisting of alkyl and aryl radicals and combinations thereof. Suitable multi-quaternary ammonium or phosphonium ions may likewise by cyclic, as in the case of the piperaziniums, and they are typically of a type in which the pentavalent nitrogen or phosphorous atoms are linked to one another by at least one divalent organic (e.g. polymethylene) radical and each further substituted by monovalent organic groups of the kind just mentioned sufficient in number (normally two or three) that four fifths of the valence of each such pentavalent atom is satisfied by such divalent and monovalent organic radicals. As such monovalent organic radicals, suitable aryl groups contain typically from six to twelve carbon atoms and preferably only one aromatic ring as in, for example, a phenyl or benzyl radical, and suitable alkyl groups can be straight-chain, branched or cyclic with each typically containing from one to twelve carbon atoms. Although quaternary ammonium or phosphonium cations containing a combination of such alkyl and aryl groups (e.g. benzyltriethylammonium or -phosphonium ions) can be used, many embodiments of the invention are carried out with quaternary cations having no olefinic or aromatic unsaturation. Good results are generally obtained with tetraalkylammonium or tetraalkylphosphonium ions containing at least three C -C alkyl groups and a total of from 8 to 24 carbon atoms in the four alkyl groups, e.g. tetraethyl-, ethyltripropyl-, ethyltributyl-, ethyltriamyl-, ethyltrihexyl-, octyltriethyl-, tetrapropyl-, methyltripropyl-, decyltripropyl-, methyltributyl-, tetrabutyl-, amyltributyl-, tetraamyl-, tetrahexyl-, ethyltrihexyl-, diethyldioctylammonium or -phosphonium and many others referred to in the aforecited U.S. Pat. No. 3,l93,475-79 and '48 l ,14 83. Generally most practical from the economic standpoint are those tetraalkylammonium ions in which each alkyl group contains from two to five carbon atoms, e.g. diethyldiamyl-, tetrapropyl-, tetrabutyl-, amyltripropyl-, tetraamylammonium, etc., and those C -C tetraalkylphosphonium ions containing at least three C -C alkyl groups, e.g. methyltributyl-, tetrapropyl-, ethyltriamyl-, octyltriethylphosphonium, etc. Particularly useful are the C -C tetraalkylphosphonium ions containing at least three C -C alkyl groups. Similarly good results are obtained by use of the divalent polymethylenebis(trialkylammonium or trialkylphosphonium) ions, particularly those containing a total of from 17 to 36 carbon atoms and in which each trialkylammonium or trialkylphosphonium radical contains at least two C -C alkyl groups and the polymethyleneradical is C -C l i.e., a straight chain of from three of eight methylene radicals. Presently most attractive from the economic standpoint are the C -C polymethylenebis(trialkylammonium or trialkylphosphonium) ions in which each trialkylammonium or trialkylphosphonium radical contains at least two C -C alkyl groups and the polymethylene radical is C -C In many embodiments of the invention employing such polymethylenebis(trialkylammonium) ions, the carbon atom content of such ions is preferably from 20 to 34. Presently of specific interest for potential commercial use in the process of this invention are the C -C hexamethylenebis(trialkylammonium) ions, e.g. those in which each trialkylammonium radical contains at least two C -C alkyl groups, partly because water-soluble salts of such cations can be relatively simply prepared from hexamethylenediamine which is readily available in commercial quantities at relatively lost cost. Also generally preferred are the hexamethylenebis(trialkylammonium or trialkylphosphonium) ions containing from 20 to 30 carbon atoms, e.g. those in which each trialkylammonium or trialkylphosphonium radical contains at least two C -C alkyl groups, and especially the C -C hexamethylenebis(trialkylammonium) ions in which each trialkylammonium radical contains at least one and preferably two n-butyl groups. Any of such cations can be incorporated into the aqueous solution to be electrolyzed in any convenient manner, e.g. by dissolving the hydroxide or a salt (e.g. a C -C alkylsulfate) of the desired quaternary ammonium or phosphonium cation(s) in the solution in the'amount required to provide the desired concentration of such cations. One significant advantage of the polymethylenebis(- trialkylammonium or trialkyphosphonium) ions for use in the present invention is that relative to most of the corresponding tetraalkylammonium and tetraalkylphosphonium ions of the type described hereinbefore, they tend to distribute themselves in higher proportion toward the aqueous phase of a mixture of an aqueous solution of the type electrolyzed in accordance with the present invention and the undissolved organic phase which, as aforesaid, may be present in the aqueous solution during the electrolysis. Whether or not such an organic phase is present in substantial proportion in the aqueous solution during the electrolysis, product hydrodimer is generally most conveniently removed from the electrolyzed solution by adding to the solution (either before or after the electrolysis) an amount of the olefinic starting material in excess of its solubility therein, mixing the solution and the excess olefinic compound until they are substantially equilibrated, and then separating (e.g. decanting) from the resulting mixture a first portion thereof that is richer than said mixture in the olefinic compound and therefore richer than said mixture in the hydrodimer product which is normally substantially more soluble in the olefinic compound than in the electrolyzed aqueous solution. Normally, the hydrodimer product is separated from said first portion of the mixture (e.g. by distillation) while a second portion of the mixture comprising an aqueous solution of the type subjected to electrolysis in accordance with the present invention is recycled and the aqueous solution comprised by said second portion is subjected to more of such electrolysis. In process embodiments in which the hydrodimer product is separated from the electrolyzed solution in the manner just described and in view of the importance of having sufficient quaternary ammonium or phosphonium cations in the aqueous solution to maintain a high hydrodimer selectivity on further electrolysis of the solution, the use of a quaternary cation that distributes itself in relatively high proportion in the aqueous portion of a substantially equilibrated mixture of the type just described is highly attractive from the standpoint of lessening the costs of recovering such cations from the separated (e.g. decanted) organic portion of the mixture and/or loss of such cations due to incomplete recovery from said organic portion of the mixture. Surprisingly,

and despite their generally higher carbon content, various bis-quaternary cations of the class defined hereinbefore have been found to distribute themselves toward the aqueous solution in ratios significantly higher (e.g. up to at least 3-4 times higher) than those of the corresponding mono-quaternary cations.

The alkali metal salts which can be employed in the invention are those of sodium, potassium, lithium, cesium and rubidium. Generally preferred for economic reasons are those of lithium and especially sodium and potassium. Also preferred for such use are the alkali metal salts of inorganic and/or polyvalent acids, e.g. an alkali metal orthophosphate, borate or carbonate, and particularly an incompletely-substituted salt of that type, i.e. a salt in which the anion has at least one valence satisfied by hydrogen and at least one other valence satisfied by an alkali metal. Examples of such salts include disodium phosphate (Na i-IP potassium acid phosphate (Kl-I PO sodium bicarbonate (NaHCO and dipotassium borate (K HBO Also useful are the alkali metal salts of condensed acids such as pyrophosphoric, metaphosphoric, metaboric, pyroboric and the like (e.g. sodium pyrophosphate, potassium metaborate, etc.). Depending on the acidity of the aqueous solution to be electrolyzed, the stoichiometric proportions of such anions and alkali metal cations in the solution may correspond to a mixture of two or more of such salts, e.g. a mixture of sodium acid phosphate and disodium phosphate, and accordingly, such mixtures of salts (as well as mixtures of salts of different alkali metals and/or different acids) are intended to be within the scope of the expression alkali metal phosphate, borate or carbonate as used herein. In fact, it has been found that the rates of corrosion of the carbon steel anodes employed in the process of this invention are significantly and surprisingly lower when the electrolyzed solution has dissolved therein certain mixtures of such salts including most notably an alkali metal phosphate and an alkali metal borate. Any of the alkali metal salts may be dissolved in the aqueous solution as such or otherwise, e.g. as the alkali metal hydroxide and the acid necessary to neutralize the hydroxide to the extent of the desired acidity of the aqueous solution.

The concentration of alkali metal salt in the solution should be at least sufficient to substantially increase the electrical conductivity of the solution above its conductivity without such a salt being present. In general, there is also enough alkali metal salt dissolved in the solution to provide alkali metal cations constituting more than half of the total weight of all cations in the solution. In most cases, the solution has dissolved therein at least about 0.1 percent of alkali metal salt. More advantageous conductivity levels are achieved when the solution has dissolved therein at least about 1 percent of alkali metal salt or, even more preferably, at least about 2 percent of such a salt. In many cases, optimum process conditions include the solution having dissolved therein more than 5 percent (typically at least 5.5 percent) of alkali metal salt. The maximum amount of alkali metal salt in the solution is limited only by its solubility therein, which varies with the particular salt employed. With salts such as sodium or potassium phosphates and/or borates, it is generally most convenient when the solution contains between about 1 percent and about 15 percent of such a saltor mixture thereof. When the solution contains an alkali metal phosphate and an alkali metal borate, especially low rates of anode corrosion are normally achieved when the solution has dissolved therein at least about 0.5 percent and preferably at least about 2 percent of alkali metal phosphate and at least about 0.25 percent prefe rably at least about 0.5 percent but in some cases desirably not more than about 4 percent of alkali metal borate.

The acidity of the solution is preferably such that a neutral or alkaline condition prevails at the cathode. Since there is normally an acidity gradient across the cell, pH at the anode can be lower than seven, if desired. In most cases, however, pH of the overall solution is at least about five, preferably at least about six and most conveniently at least about seven. Also in most cases, the overall solution pH is not higher than about twelve, typically not higher than about eleven and, with the use of sodium or potassium phosphates and/0r borates as the main conductive salts, generally not substantially higher than about ten.

The temperature of the solution may be at any level compatible with existence as such of the solution itself, i.e., above its freezing point but below its boiling point under the pressure employed. Good results can be achieved between about 5 and about C or at even higher temperatures if pressures substantially above one atmosphere are employed. The optimum temperature range will vary with the specific olefinic compound and hydrodimer, among other factors, but in hydrodimerization of acrylonitrile to adiponitrile, electrolysis temperatures of at least about 25 are usually preferred and those between about 40 and about 65C. are especially desirable. In fact, it is an important advantage of the present invention that it can be carried out at such relatively high temperatures without an economically intolerable rate of anode corrosion.

Although not necessary, a liquid-impermeable cathode is usually preferred. With the use of such a cathode, the aqueous solution to be electrolyzed is generally passed between the anode and cathode at a linear velocity with reference to the adjacent electrode surface of at least about 0.6 meter per second and even more preferably between about 0.9 and about 2.44 meters per second although a solution velocity up to 6 meters per second or higher can be employed, if desired. The gap between the anode and cathode can be very narrow, e.g. about 1.0 millimeter or less, or as wide as l .27 centimeters or even wider, but is usually most conveniently of a width between about 1.5 and about 6.35 millimeters.

As is well-known, electrolytic hydrodimerization of an olefinic compound having a formula as set forth hereinbefore must be carried out in contact with a cathodic surface having a cathode potential sufficient for hydrodimerization of that compound. In the process of this invention, the cathodic surface can be made of virtually any material at which such a cathode potential can be provided and which is not dissolved, corroded or fouled by the electrolysis medium at an intolerable rate. In general, the process is most desirably carried out with a cathode consisting essentially of cadmium, mercury, thallium, lead, zinc, tin (possibly not suitable with some nitrile starting materials) or graphite, by which is meant that the cathodic surface contains a high percentage (generally at least about percent and preferably at least about 98 percent) of one or a combination (e.g. an alloy) of two or more of such materials, but it may contain a small amount of one or more other constituents that do not alter the nature of the cathodic surface so as to prevent substantial realization of the advantages of the present invention, particularly as described herein. Such other constituents, if present, are desirably other materials having relatively high hydrogen overvoltages. Of particular preference are cathodes consisting essentially of cadmium, mercury, thallium, lead or an alloy of at least one of such metals, and especially cathodes consisting essentially of cadmium. Cathodes employed in this invention can be prepared by various techniques such as, for example, electroplating of the desired cathode material on a suitably-shaped substrate of some other material, e.g. a metal having greater structural rigidity, or by chemically, thermally and/or mechanically bonding a layer of the cathode material to a similar substrate. Alternatively, a plate, sheet, rod or any other suitable configuration consisting essentially of the desired cathode material may be used without such a substrate, if convenient.

As aforesaid, the process of this invention is carried out in an electrolytic cell having an anode consisting essentially of carbon steel. By that is meant that the portion of the positive pole of the cell that is in contact with the solution undergoing electrolysis consists essentially of a steel of a type conventionally recognized as a carbon steel and not as iron or an alloy steel or stainless steel. A standard definition of carbon steel, provided by the American Iron and Steel Institute (A151) is as follows: Carbon steel is classed as such when no minimum content is specified or guarenteed for aluminum, chromium, columbium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium; when the minimum for copper does not exceed 0.40 percent; or when the maximum content specified or guaranteed for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60 Carbon steels of various compositions are listed in the 1000, 1100 and 1200 series of A181 and SAE standard steel composition numbers, many of which may be found on page 62 of Volume 1, Metals Handbook, 8th Edition (1961) published by the American Society for Metals, Metals Park, Ohio. Carbon steels are readily distinguishable from steels conventionally known as alloy steels and listed in the 1300 and higher series of the aforementioned standard steel composition numbers, from the special alloy steels that are conventionally known as stainless steels and normally contain substantial (usually more than 0.5 percent) other metals such as nickel and/or chromium, and from commerciallypure iron which, by definition, contains not more than about 0.01 percent carbon. In general, the carbon steels that can be used as anode materials in the process of this invention contain between about 0.02 percent carbon (more typically at least about 0.05 percent carbon) and about 2 percent carbon. Normally, carbon steels such as those of the A181 and SAE 1000 series of standard steel composition numbers are preferred and those containing between about 0.1 percent and about 1.5 percent carbon are typically most desirable. Such proportions are expressed, of course, without reference to any constituents of the electrolysis medium although in operation of the process, certain of those constituents may become associated with the surface of the anode, either transiently or otherwise, so'as to act as a part of the anodic surface in the sense of serving as the positive pole of the electrolytic cell. For example, in some embodiments of the process, it may be desirable to include in the electrolysis medium a small amount (generally between about 0.01 percent and about 3 percent) of an inhibitor of corrosion of the anode (e.g. an alkali metal salt of a condensed phosphoric acid, such as tetrasodium pyrophosphate or the like) and/or a similarly small amount of a heavy metal chelating agent (e.g. an alkali metal salt of a nitrilocarboxylic acid, such as tetrasodium ethylenediaminetetraacetate or -tetrapropionate, trisodium hydroxyethylethylenediaminetriacetate, trisodium nitrilotriacetate or the like) and one or both of the same may in some cases (generally in only very minor quantities) become so associated with the carbon steel anode surface.

In operation of the undivided cell, in which an anode and a cathode of the cell are simultaneously in direct physical contact with the solution being electrolyzed, each anode may be in the form of a plate, sheet, strip, rod or any other suitable configuration. In a preferred embodiment, the anode is a sheet of carbon steel closely spaced from and essentially parallel to a sheetlike cathode in the same cell. As typically used in the process of this invention, carbon steel anodes are relatively inexpensive, highly conductive, have good mechanical properties including excellent structural strength and, as aforesaid, corrode at a rate that is lower, to a surprisingly great degree, than the corrosion rate of anode materials previously suggested for similar use. The corrosion rate of the carbon steel anode is particularly and importantly lower at relatively high current densities, permitting much greater hydrodimer productivity in a cell having a given anode surface area in contact with the electrolysis medium and thereby available for passage of the electric current employed in the process of this invention.

In general, there is no minimum current density with which the present process can be carried out but economic considerations usually require the use of a current density of at least about 0.01 and preferably at least about 0.05 amp per square centimeter (amp/cm of the anode surface in contact with the solution being electrolyzed. Similar processes employing more readily corroded anodes have had to be generally carried out, as aforesaid, with current densities substantially lower than 0.1 amp/cm of such anode surface, but the present process can be very conveniently carried out with anode current densities of at least about 0.1 amp/cm and, usually even more desirably from an economic standpoint, with anode current densities of at least about 0.15 amp/cmphu 2 or even much higher. Although greater anode current densities may be practical in some instances, those employed in the present process are generally not higher than about 0.75 amp/cm and even more typically not higher than about 0.5 amp/cm of the anode surface area in contact with the solution being electrolyzed. Depending on other process variables, anode current densities of not more than about 0.35 amp/cm may be preferred in some embodiments of the invention. However, the fact that any of the aforementioned anode current densities of at least about 0.1, and particularly at least about 0.15 amp/cm can be advantageously employed in the process of this invention, and especially at temperatures higher than about 25C., e.g. from about 40 up to about 65C. or even higher, is very surprising in view of the much greater corrosion of other anode materials such as iron, magnetite, etc., in similar process use but under conditions generally considered far less corrosive, e.g. at much lower temperatures and/or anode current densities. As will be readily apparent, the use of carbon steel anodes having advantages of that magnitude in a process from which there are available hydrodimerization selectivities of at least about 75 percent, typically at least about 80 percent and commonly as high as 85 percent or even higher has provided that process with a significant and unexpected commercial utility. In addition, carbon steel does not contain substantial proportions of other metals (such as nickel, etc.) which are present in stainless and other alloy steels and which, if released into the electrolysis medium, e.g. by corrosion of an anode containing such metals, may tend to plate out or otherwise become deposited on the cathode and thereon alter the nature of the cathodic surface so as to increase the generation of saturated starting material (e.g. propionitrile) at the expense of hydrodimer selectivity.

The following specific examples of the process of this invention are included for purposes of illustration only and do not imply any limitations on the scope of the invention. Also in the following Examples, acrylonitrile and adiponitrile are generally represented by AN and ADN, respectively.

EXAMPLE 1 In a continuous process, an aqueous solution having dissolved therein an average of approximately 1.0% AN, 1.1% ADN, 0.2% AN EHD byproducts, 8 X gram mol per liter of ethyltributylammonium cations, 10 percent of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9 and 0.4 percent of a disodium salt of ethylenediaminetetraacetic acid (Na c H N O ll-l O) was circulated at 50-55C. and a velocity of 1.37 meters per second through an undivided electrolytic cell having an AlSl 1020 (0.2 percent) carbon steel anode separated by a gap of 2.72 millimeters from a cathode composed of cadmium conforming to ASTM Designation B440- 66T issued 1966 (at least 99.9 percent Cd). The solution, which also had entrained therein approximately 4 percent by weight of an organic phase containing an average of about 62% ADN, 20% AN, 10% AN EHD byproducts and 8 percent water, was electrolyzed as it passed through the cell with a voltage drop across the cell averaging 4.25 volts and a current density averaging 0.23 amplcm of anode (or cathode) surface in contact with the solution and then fed into a decanter for equilibration with an accumulated upper layer having approximately the composition of the aforedescribed organic phase and withdrawal of equilibrated lower (aqueous) layer for recycle through the cell. After 213 hours of electrolysis during which AN and water were continuously added to the circulating aqueous solution and an equivalent amount of the organic phase containing product ADN, byproducts and unreacted AN was removed, it was found than AN in the solution had been converted to ADN with an average selectivity of at least 87.5 percent and the carbon steel anode had corroded at the average rate of only 0.97 millimeter per year.

EXAMPLE n In a continuous process, an aqueous solution having dissolved therein approximately 1.7% AN, 1.2% ADN, 0.2% AN EHD byproducts, 9.5 X 10 gram mol per liter of ethyltributylammonium cations, 10 percent of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9, 0.1 percent of a ferrous metal corrosion inhibitor (tetrasodium pyrophosphate) and 0.05 percent of a disodium salt of ethylenediaminetetraacetic acid (Na C l-l N O .2l-l O) was circulated at a temperature of 55C. and a velocity between 1.22 and 1.37 meters per second through an undivided electrolytic cell having an AlSl 1020 (0.2 percent) carbon steel anode separated by a gap of 2.39 millimeters from a cadmium cathode having the composition described in Example 1. The solution, which also had entrained therein approximately 0.8 percent by weight of an organic phase containing about 52% ADN, 31% AN, 9% AN EHD byproducts and 8 percent water, was electrolyzed as it passed through the cell with a voltage drop across the cell of 4.4 volts and a current density of 0.27 amp/cm of anode (or cathode) surface in contact with the solution and the fed into a decanter for equilibration with an accumulated upper layer having approximately the composition of the aforedescribed organic phase and when withdrawal of equilibrated lower (aqueous) layer for recycle through the cell. After 490 hours of electrolysis during which AN and water were continuously added to the circulating aqueous solution and an equivalent amount of organic phase containing product ADN, byproducts and unreacted AN was removed it was found that AN in the solution had been converted to ADN with an average selectivity of 86.3% and the carbon steel anode had corroded at the average rate of only 0.86 millimeter per year.

EXAMPLE III In a continuous process, an aqueous solution having dissolved therein an average approximately 1.5% AN, 1.2% ADN, 0.2% AN EHD byproducts, 6.8 X 10 gram mol per liter of ethyltributylammonium cations, 10 percent of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9, 1.5 percent of sodium pyroborate (Na B O and 0.1 percent of sodium nitrate was circulated at 55C. and a velocity of 1.22 meters per second through an undivided electrolytic cell having an AlSI 1020 (0.2 percent) carbon steel anode separated by a gap of 2.36 millimeters from a cadmium cathode having the composition described in Example I. The solution, which also had entrained therein approximately 0.8 percent by weight of an organic phase containing an average of about 55% ADN, 28% AN, 9% AN EHD byproducts and 8 percent water, was electrolyzed as it passed through the cell with a voltage drop across the cell averaging 3.8 volts and a current density averaging 0.15 amp/cm of anode (or cathode) surface in contact with the solution and then fed into a decanter for equilibration with an accumulated upper layer having approximately the composition of the aforedescribed organic phase and withdrawal of equilibrated lower (aqueous) layer for recycle through the cell. After about hours of electrolysis during which AN and water were continuously added to the circulating aqueous solution and an equivalent amount of organic phase containing product ADN, byproducts and reacted AN was removed, it was found that AN in the solution had been converted to adiponitrile with an average selectivity of about 89 percent and the carbon steel anode had corroded at the average rate of only 0.41 millimeter per year.

EXAMPLE IV In a continuous process, an aqueous solution having dissolved therein approximately 1.4% AN, 1.2% ADN, 0.2% AN El-lD byproducts, 6.8 X gram mole per liter of ethyltributylammonium cations, 10 percent of a mixture of incompletely-substituted sodium orthophosphates corresponding to the solution pH of 9, 2 percent of sodium pyroborate (Na B O and 0.4percent of tetrasodium ethylenediaminetetraacetate (Na EDTA) was circulated at 55C. and a velocity of 1.22 meters per second through an undivided electrolytic cell having an A181 1020 (0.2 percent) carbon steel anode separated by a gap of 2.36 millimeters from a cadmium cathode having the composition described in Example 1. The solution, which also had entrained therein approximately 0.8 percent by weight of an organic phase containing about 58% ADN, 25.5% AN, 8.5% AN EHD byproducts and 8 percent water, was electrolyzed as it passed through the cell with a voltage drop across the cell averaging 3.85 volts and a current density of 0.16 amp/cm of anode (or cathode) surface in contact with the solution and then fed into a decanter for equilibration with an accumulated upper layer having approximately the composition of the aforedescribed organic phase and withdrawal of equilibrated lower (aqueous) layer for recycle through the cell. After 288 hours of electrolysis during which acrylonitrile and water were continuously added to the circulating aqueous solution and an equivalent amount of organic phase containing product ADN, byproducts and unreacted AN was removed, it was found that AN in the solution had been converted to adiponitrile with an average selectivity of 87.7 percent and the carbon steel anode had corroded at the average rate of only 0.38 millimeter per year.

EXAMPLE V In a continuous process, a liquid electrolysis medium composed between 85.9 percent and 87.5 percent by (1) an aqueous solution having dissolved therein between l.4% and 1.6% AN, about 1.2% ADN, 9.6-9.9% of a mixture of sodium orthophosphates, 0.8-2.5 X 10 mol per liter of ethyltributylammonium ions, about 0.6 percent of tetrasodium ethylenediaminetetraacetate (Na EDTA) and the sodium borates produced by neutralizing orthoboric acid in an amount corresponding to about 2 percent of the solution to the solution pH of 8.5-9 and between 12.5 percent and 14.1 percent by (2) a dispersed but undissolved organic phase containing 26-29% AN, 54-59% ADN, 7-9% AN EHD byproducts and 8 percent water was circulated at 55C. and 1.16 meters per second through an undivided electrolytic cell having an A151 1020 carbon steel anode separated by a gap of 2.25 millimeters from a cathode composed of a rolled sheet of cadmium conforming to ASTM Designation B440-66T (at least 99.9 percent Cd) and electrolyzed as it passed through the cell with a current density of 0.2 amp/cm of the surface of the anode (or cathode). Organic phase containing product ADN, an EHD byproducts and unreacted AN was separated from the electrolyzed medium and makeup AN was added after which the medium was recirculated through the cell and electrolyzed again under the conditions just described. For each Faraday of current passed through the medium, 0.475 millimol of Na EDTA was added to the circulating medium and about 10 grams of the solution were purged from the system and replaced with water containing sufficient dissolved ethyltributylammonium ions and sodium orthophosphates and borates to maintain the concentrations of those constituents of the solution at the aforedescribed levels and thetotal volume of the medium essentially constant. After 268 hours of electrolysis under those conditions, it was found that AN had been converted to ADN with average and final selectivities of 87-88 percent and the steel anode had corroded at the average rate of 0.5 millimeter per year.

EXAMPLE VI In a continuous process, a liquid electrolysis medium composed about 99 percent by (1) an aqueous solution having dissolved therein between 1.4% and 1.6% AN, about 1.2% ADN, 10 percent of a mixture of sodium orthophosphates, 0.6-1.4 X 10 mol per liter of methyltributylphosphonium ions, about 0.5 percent of Na EDTA and the sodium borates produced by neutralizing orthoboric acid in an amount corresponding to about 2 percent of the solution to the solution pH of about 8.5 and about 1 percent by (2) a dispersed but undissolved organic phase containing 27-29% AN, 54-58% ADN, 7-9% AN EHD byproducts and 8 percent water was circulated at 55C. and 1.22 meters per second through an undivided electrolytic cell having an AlSl 1020 carbon steel anode separated by a gap of 1.76 millimeters from a cadmium cathode essentially the same as that used in Example V and electrolyzed as it passed through the cell with a current density of 0.185 amp/cm of the surface of the anode (or cathode). Organic phase containing product ADN, AN El-lD byproducts and unreacted AN was separated from the electrolyzed medium and make-up AN was added after which the medium was recirculated through the cell and electrolyzed again under the conditions just described. For each Faraday of current passed through the medium, 0.4 millimol of Na EDTA was added to the circulating medium and about 12 grams of the solution were purged from the system and replaced with water containing sufficient dissolved methyltributylphosphonium ions and sodium orthophosphates and borates to maintain the concentrations of those consitituents of the solution at the aforedescribed levels and the total volume of the medium essentially constant. After hours of electrolysis under those conditions, it was found that AN had been converted to ADN with average and final selectivities of 88 percent and the steel anode had corroded at an average rate substantially lower than 0.5 millimeter per year.

EXAMPLE Vll In a process essentially as described in Example Vl except that the quaternary cations in the aqueous solution were O.27.9 X 10 mol per liter of hexamethylenebis(ethyldibutylammonium) ions instead of the 0.6-1.4 X 10 mol per liter of methyltributylphosphonium ions, it was found after 330 hours of electrolysis that AN had been converted to ADN with average and final selectivities of 88-98 percent and the steel anode had corroded at an average rate substantially lower than 0.5 millimeter per year.

EXAMPLE VIII In a process essentially as described in Example VI except that the quaternary cations in the aqueous solution were 0.4-2.6 X 10 mol per liter of tetramethylenebis(tributylammonium) ions instead of the 0.6l.4 X 10* mol per liter of methyltributylphosphonium ions, it was found after 171 hours of electrolysis that AN had been converted to ADN with average and final selectivities of 87-88 percent and the steel anode had corroded at an average rate substantially lower than 0.5 millimeter per year.

It is apparent from the foregoing examples that although the rate of corrosion of the carbon steel anode is surprisingly low when the electrolysis medium contains an alkali metal phosphate but no alkali metal borate (e.g. 0.97 and 0.86 millimeter per year in Examples I and II), the rate of such corrosion is significantly and even more surprisingly further lowered when the electrolysis medium contains an alkali metal phosphate and an alkali metal borate (e.g. to 0.41 and 0.38 millimeter per year in Examples III and IV and no higher than 0.5 millimeter per year in any of Examples Ill Vlll).

We claim:

1. A process for hydrodimerizing an olefinic compound having the formula R C=CR-X wherein -X is -CN, -CONR or -COOR, R is hydrogen or R, R is C -C alkyl and at least one R directly attached to either of the two carbon atoms joined by the double bond in said formula is hydrogen which comprises electrolyzing an aqueous solution having dissolved therein at least about 0.1 percent by weight of said olefinic compound, quaternary ammonium ions in a concentration between about 10 and about 0.5 gram mol per liter and at least about 0.1% by weight of alkali metal phosphate, borate or carbonate in an undivided cell having an anode consisting essentially of carbon steel containing between about 0.02 percent about 2 percent by weight of carbon, said solution having a pH of at least about 5.

2. The process of claim 1, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.

3. The process of claim I, said solution having dissolved therein more than 5 percent by weight of the alkali metal phosphate, borate or carbonate.

4. The process of claim 1, said solution having dissolved therein at least about 0.5 percent by weight of said olefinic compound, between about and about 10 gram mol per liter of C -C tetraalkylammonium ions containing at least three C -C alkyl groups and at least about 1 percent by weight of the alkali metal phosphate, borate or carbonate.

5. The process of claim 4, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.

6. The process of claim 1, said solution having dissolved therein at least about 0.5% by weight of said olefinic compound, between about 10' and about 10 gram mol per liter of C -C polymethylenebis(trialkylammonium) ions in which each trialkylammonium radical contains at least two C -C alkyl groups and the polymethylene radical is C -C and at least about 1 percent by weight of the alkali metal phosphate, borate or carbonate.

7. The process of claim 6, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.

8. The process of claim 1 wherein the olefinic compound is acrylonitrile, said solution having dissolved therein at least about 0.5 percent but less than about 5 percent by weight of acrylonitrile, between about 10 and about 10 gram mol per liter of quaternary ammonium ions and at least about 1 percent by weight of sodium or potassium salt selected from the group consisting of phosphate, borate and carbonate and wherein the solution is electrolyzed in said cell with a current density of at least about 0.05 amp/cm of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 5 and about C.

9. The process of claim 8, said solution having dissolved therein more than 5 percent by weight of the sodium or potassium salt.

10. The process of claim 8, said solution having dissolved therein between about 1 percent and about 4 percent by weight of acrylonitrile, between about 10 and about 10' gram mol per liter of quaternary ammonium ions selected from the group consisting of C -C tetraalkylammonium ions containing at least three C -C alkyl groups and C -,-C polymethylenebis(- trialkylammonium) ions in which each trialkylammonium radical contains at least two C -C alkyl groups and the polymethylene radical is C -C and at least about 1 percent by weight of sodium or potassium salt selected from the group consisting of phosphate and borate and wherein the solution is electrolyzed in said cell with a current density between about 0.1 and about 0.5 amp/cm of the surface of said anode in contact with the solution, said solution having a temperature between about 25 and about 65C.

11. The process of claim 10, said solution having dissolved therein more than 5 percent by weight of the sodium or potassium salt.

12. The process of claim 11, said solution having a pH between about 7 and about 11 and a temperature of at least about 40C.

13. The process of claim 10, wherein the aqueous solution is electrolyzed in an electrolysis medium consisting essentially of said solution and up to about 20 percent by weight of an undissolved organic phase.

14. A process for hydrodimerizing an olefinic compound having the formula R C=CR-X wherein -X is -CN, -CONR or -COOR', R is hydrogen or R, R is C -C alkyl and at least one R directly attached to either of the two carbon atoms joined by the double bond in said formula is hydrogen which comprises electrolyzing an aqueous solution having dissolved therein at least about 0.1 percent by weight of said olefinic compound, quaternary phosphonium ions in a concentration between about 10" and about 0.5 gram mol per liter and at least about 0.1 percent by weight of alkali metal phosphate, borate or carbonate in an undivided cell having an anode consisting essentially of carbon steel containing between about 0.02 percent and about 2 percent by weight of carbon, said solution having a pH of at least about 5.

15. The process of claim 14, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.

16. The process of claim 14, said solution having dissolved therein more than percent by weight of the alkali metal phosphate, borate or carbonate.

17. The process of claim 14, said solution having dissolved therein at least about 0.5 percent by weight or said olefinic compound, between about and about 10' gram mol per liter of C -C tetraalkylphosphonium ions containing at least three C -C alkyl groups and at least about 1% of the alkali metal phosphate, borate or carbonate.

18. The process of claim 17 wherein the olefinic compound is acrylonitrile, said solution having dissolved therein less than 5 percent by weight of acrylonitrile and more than 5 percent by weight of alkali metal phosphate or borate and wherein the solution is electrolyzed in said cell with a current density between about 0.1 and about 0.5 amp/cm of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 40 and about 65C.

19. A process for hydrodimerizing an olefinic compound having the formula R C=CR-X wherein -X is -CN, -CONR or -COOR, R is hydrogen or R, R is C -C alkyl and at least one R directly attached to either of the two carbon atoms joined by the double bond in said formula is hydrogen which comprises electrolyzing an aqueous solution having dissolved therein at least about 0.1 percent by weight of said olefinic compound, quaternary ammonium ions in a concentration between about 10 and about 0.5 gram mol per liter, at least about 0.5 percent by weight of alkali metal phosphate and at least about 0.25 percent by weight of alkali metal borate in an undivided cell having an anode consisting essentially of carbon steel containing between about 0.02 percent and about 2 percent by weight of carbon with a current density of at least 0.05 amp/cm of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 25 and about 75C.

20. The process of claim 19, said solution having dissolved therein at least about 0.5 percent but less than about 5 percent of said olefinic compound and between about 0.5 percent and about 4 percent by weight of sodium or potassium borate.

21. The process of claim wherein the solution is electrolyzed with between about 0.1 and about 0.5 amp/cm of the surface of said anode in contact with the solution, said solution having a pH between about 7 and about l0 and a temperature between about 40 and about 65C.

22. The process of claim 21, said solution having dissolved therein between about 10" and about 10 gram mol per liter of quaternary ammonium ions selected from the group consisting of C -C tetraalkylammonium ions containing at least three C -C alkyl groups and C -C polymethylenebis(trialkylammonium) ions in which each trialkylammonium radical contains at least two C -C alkyl groups and the polymethylene radical is C -C and at least about 5% by weight of sodium or potassium phosphate.

23. The process of claim 22 wherein the olefinic compound is acrylonitrile.

24. A process for hydrodimerizing an olefinic compound having the formula R C=CR-X wherein -X is -CN, CONR or -COOR', R is hydrogen or R, R is C -C alkyl and at least one R directly attached to either of the two carbon atoms joined by the double bond in said formula is hydrogen which comprises electrolyzing an aqueous solution having dissolved therein at least about 0.1 percent by weight of said olefinic compound, quaternary phosphonium ions in a concentration between about 10' and about 0.5 gram mol per liter, at least about 0.5 percent by weight of alkali metal phosphate and at least about 0.25 percent by weight of alkali metal borate in an undivided cell having an anode consisting essentially of carbon steel containing between about 0.02 percent and about 2 percent by weight of carbon with a current density of at least about 0.05 amp/cm of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 25 and about C.

25. The process of claim 24, said solution having dissolved therein at least about 0.5 percent but less than about 5 percent of said olefinic compound and between about 0.5 percent and about 4 percent by weight of sodium or potassium borate.

26. The process of claim 25 wherein the solution is electrolyzed with between about 0.1 and about 0.5 amp/cm of the surface of said anode in contact with the solution, said solution having a pH between about 7 and about 10 and a temperature between about 40 and about 65C.

27. The process of claim 26 wherein the olefinic compound is acrylonitrile, said solution having dissolved therein between about l0 and about 10* gram mol per liter of C -C tetraalkylphosphonium ions containing at least three C -C alkyl groups and at least about 5 percent by weight of sodium or potassium phosphate. 

1. A PROCESS FOR HYDRODIMERIZING AN OLEFINIC COMPOUND HAVING FORMULA R2C=CR-X WHEREIN -X IS -CN, -CONR2 OR -COOR'', R IS HYDROGEN OR R'', R'' IS C1-C4ALKYL AND AT LEAST ONE R DIRECTLY ATTACHED TO EITHER OF THE TWO CARBON ATOMS JOINED BY THE DOUBLE BOND IN SAID FORMULA IS HYDROGEN WHICH COMPRISES ELECTROLYZING AN AQUEOUS SOLUTION HAVING DISSOLVED THEREIN AT LEAST ABOUT 0.1 PERCENT BY WEIGHT OF SAID OLEFINE COMPOUND, QUATERNARY AMMONIUM IONS IN A CONCENTRATION BETWEEN ABOUT 10-5 AND ABOUT 0.5 GRAM MOL PER LITER AND AT LEAST ABOUT 0.1% BY WEIGHT OF ALKALI METAL PHOSPHATE, BORATE OR CARBONATE IN AN UNDIVIDED CALL HAVING AN ANODE CONSISTING ESSENTIALLY OF CARBON STEEL CONTAINING BETWEEN ABOUT 0.02 PERCENT ABOUT 2 PERCENT BY WEIGHT OF CARBON, SAID SOLUTION HAVING A PH OF AT LEAST ABOUT
 5. 2. The process of claim 1, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.
 3. The process of claim 1, said solution having dissolved therein more than 5 percent by weight of the alkali metal phosphate, borate or carbonate.
 4. The process of claim 1, said solution having dissolved therein at least about 0.5 percent by weight of said olefinic compound, between about 10 4 and about 10 1 gram mol per liter of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and at least about 1 percent by weight of the alkali metal phosphate, borate or carbonate.
 5. The process of claim 4, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.
 6. The process of claim 1, said solution having dissolved therein at least about 0.5% by weight of said olefinic compound, between about 10 5 and about 10 1 gram mol per liter of C17-C36 polymethylenebis(trialkylammonium) ions in which each trialkylammonium radical contains at least two C3-C6 alkyl groups and the polymethylene radical is C3-C8 and at least about 1 percent by weight of the alkali metal phosphate, borate or carbonate.
 7. The procesS of claim 6, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.
 8. The process of claim 1 wherein the olefinic compound is acrylonitrile, said solution having dissolved therein at least about 0.5 percent but less than about 5 percent by weight of acrylonitrile, between about 10 5 and about 10 1 gram mol per liter of quaternary ammonium ions and at least about 1 percent by weight of sodium or potassium salt selected from the group consisting of phosphate, borate and carbonate and wherein the solution is electrolyzed in said cell with a current density of at least about 0.05 amp/cm2 of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 5* and about 75*C.
 9. The process of claim 8, said solution having dissolved therein more than 5 percent by weight of the sodium or potassium salt.
 10. The process of claim 8, said solution having dissolved therein between about 1 percent and about 4 percent by weight of acrylonitrile, between about 10 4 and about 10 2 gram mol per liter of quaternary ammonium ions selected from the group consisting of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and C17-C36 polymethylenebis(trialkylammonium) ions in which each trialkylammonium radical contains at least two C3-C6 alkyl groups and the polymethylene radical is C3-C8 and at least about 1 percent by weight of sodium or potassium salt selected from the group consisting of phosphate and borate and wherein the solution is electrolyzed in said cell with a current density between about 0.1 and about 0.5 amp/cm2 of the surface of said anode in contact with the solution, said solution having a temperature between about 25* and about 65*C.
 11. The process of claim 10, said solution having dissolved therein more than 5 percent by weight of the sodium or potassium salt.
 12. The process of claim 11, said solution having a pH between about 7 and about 11 and a temperature of at least about 40*C.
 13. The process of claim 10, wherein the aqueous solution is electrolyzed in an electrolysis medium consisting essentially of said solution and up to about 20 percent by weight of an undissolved organic phase.
 14. A process for hydrodimerizing an olefinic compound having the formula R2C CR-X wherein -X is -CN, -CONR2 or -COOR'', R is hydrogen or R'', R'' is C1-C4 alkyl and at least one R directly attached to either of the two carbon atoms joined by the double bond in said formula is hydrogen which comprises electrolyzing an aqueous solution having dissolved therein at least about 0.1 percent by weight of said olefinic compound, quaternary phosphonium ions in a concentration between about 10 5 and about 0.5 gram mol per liter and at least about 0.1 percent by weight of alkali metal phosphate, borate or carbonate in an undivided cell having an anode consisting essentially of carbon steel containing between about 0.02 percent and about 2 percent by weight of carbon, said solution having a pH of at least about
 5. 15. The process of claim 14, said solution having dissolved therein less than about 5 percent by weight of said olefinic compound.
 16. The process of claim 14, said solution having dissolved therein more than 5 percent by weight of the alkali metal phosphate, borate or carbonate.
 17. The process of claim 14, said solution having dissolved therein at least about 0.5 percent by weight of said olefinic compound, between about 10 4 and about 10 2 gram mol per liter of C8-C24 tetraalkylphosphonium ions containing at least three C2-C6 alkyl groups and at least about 1% of the alkali metal phosphate, borate or carbonate.
 18. The process of claim 17 wherein the olefinic compound is acrylonitrile, said solution having dissolved therein less than 5 percent by weight of acrylonitrile and more than 5 percent by weight of alkali metal phosphate or borate and wherein the solution is electrolyzed in said cell with a current density between about 0.1 and about 0.5 amp/cm2 of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 40* and about 65*C.
 19. A process for hydrodimerizing an olefinic compound having the formula R2C CR-X wherein -X is -CN, -CONR2 or -COOR'', R is hydrogen or R'', R'' is C1-C4 alkyl and at least one R directly attached to either of the two carbon atoms joined by the double bond in said formula is hydrogen which comprises electrolyzing an aqueous solution having dissolved therein at least about 0.1 percent by weight of said olefinic compound, quaternary ammonium ions in a concentration between about 10 5 and about 0.5 gram mol per liter, at least about 0.5 percent by weight of alkali metal phosphate and at least about 0.25 percent by weight of alkali metal borate in an undivided cell having an anode consisting essentially of carbon steel containing between about 0.02 percent and about 2 percent by weight of carbon with a current density of at least 0.05 amp/cm2 of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 25* and about 75*C.
 20. The process of claim 19, said solution having dissolved therein at least about 0.5 percent but less than about 5 percent of said olefinic compound and between about 0.5 percent and about 4 percent by weight of sodium or potassium borate.
 21. The process of claim 20 wherein the solution is electrolyzed with between about 0.1 and about 0.5 amp/cm2 of the surface of said anode in contact with the solution, said solution having a pH between about 7 and about 10 and a temperature between about 40* and about 65*C.
 22. The process of claim 21, said solution having dissolved therein between about 10 4 and about 10 2 gram mol per liter of quaternary ammonium ions selected from the group consisting of C8-C24 tetraalkylammonium ions containing at least three C2-C6 alkyl groups and C17-C36 polymethylenebis(trialkylammonium) ions in which each trialkylammonium radical contains at least two C3-C6 alkyl groups and the polymethylene radical is C3-C8 and at least about 5% by weight of sodium or potassium phosphate.
 23. The process of claim 22 wherein the olefinic compound is acrylonitrile.
 24. A process for hydrodimerizing an olefinic compound having the formula R2C CR-X wherein -X is -CN, CONR2 or -COOR'', R is hydrogen or R'', R'' is C1-C4 alkyl and at least one R directly attached to either of the two carbon atoms joined by the double bond in said formula is hydrogen which comprises electrolyzing an aqueous solution having dissolved therein at least about 0.1 percent by weight of said olefinic compound, quaternary phosphonium ions in a concentration between about 10 5 and about 0.5 gram mol per liter, at least about 0.5 percent by weight of alkali metal phosphate and at least about 0.25 percent by weight of alkali metal borate in an undivided cell having an anode consisting essentially of carbon steel containing between about 0.02 percEnt and about 2 percent by weight of carbon with a current density of at least about 0.05 amp/cm2 of the surface of said anode in contact with the solution, said solution having a pH of at least about 6 and a temperature between about 25* and about 75*C.
 25. The process of claim 24, said solution having dissolved therein at least about 0.5 percent but less than about 5 percent of said olefinic compound and between about 0.5 percent and about 4 percent by weight of sodium or potassium borate.
 26. The process of claim 25 wherein the solution is electrolyzed with between about 0.1 and about 0.5 amp/cm2 of the surface of said anode in contact with the solution, said solution having a pH between about 7 and about 10 and a temperature between about 40* and about 65*C.
 27. The process of claim 26 wherein the olefinic compound is acrylonitrile, said solution having dissolved therein between about 10 4 and about 10 2 gram mol per liter of C8-C24 tetraalkylphosphonium ions containing at least three C2-C6 alkyl groups and at least about 5 percent by weight of sodium or potassium phosphate. 